Comment 2 for bug 2057948

I pushed a patch that should add an Idempotency-Key header to the Stripe /payment_intents request.

The Idempotency-Key is md5_hex(sort(transaction_ids)). This should guarantee that repeated requests to pay the same set of fines is not reposted. It will not prevent a user from paying two fines then trying to pay only the 2nd one again.